Loss of MYC and E-box3 binding contributes to defective MYC-mediated transcriptional suppression of human MC-let-7a-1~let-7d in glioblastoma.
Loss of MYC and E-box3 binding contributes to defective MYC-mediated transcriptional suppression of human MC-let-7a-1~let-7d in glioblastoma.
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MYC 和 E-box3 结合的丧失导致胶质母细胞瘤中 MYC 介导的人 MC-let-7a-1~let-7d 转录抑制缺陷。
DOI：
10.18632/oncotarget.10517
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发表时间：
2016-08-30
期刊：
影响因子：
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通讯作者：
Lin MC
中科院分区：
文献类型：
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作者：
Wang Z;Lin S;Zhang J;Xu Z;Xiang Y;Yao H;Ge L;Xie D;Kung HF;Lu G;Poon WS;Liu Q;Lin MC
我们以前报道过MYC癌蛋白下调人肝癌组织中MC-let-7a-1~let-7 d microRNA簇的转录。令人惊讶的是，计算机分析表明，let-7 miRNA表达水平在胶质母细胞瘤（GBM）中没有降低。在这里，我们研究了这种差异表达的分子基础。利用人GBM U87和U251细胞，我们首次证明了MYC的强制过表达确实不能下调GBM中人MC-let-7a-1~let-7 d microRNA簇的表达。此外，对GBM中MC-let-7a-1~let-7 d启动子的分析表明，MYC不能抑制启动子活性。用GSE 55092（HCC）和GSE 4290（GBM）的表达数据进行的Pearson相关和线性回归分析表明，MC-let-7a-1~let-7 d和MYC仅在HCC中存在匡威的关系，而在GBM中不存在这种关系。为了了解潜在的机制，我们检查了MYC是否可以结合位于MC-let-7a-1~let-7 d启动子中的非经典E-box 3。来自染色质免疫沉淀（ChIP）和超移位测定的结果清楚地证明了GBM中MYC和E-box 3结合的丧失，首次表明GBM中MYC和E-box 3结合的缺陷是导致MYC介导的MC-let-7a-1~let-7 d和潜在的其他肿瘤抑制因子的差异性转录抑制的原因。MYC和let-7分别是关键的癌蛋白和肿瘤抑制因子。了解其调节的分子机制将提供新的见解，并对GBM以及其他癌症的治疗具有重要影响。
Previously, we reported that MYC oncoprotein down-regulates the transcription of human MC-let-7a-1~let-7d microRNA cluster in hepatocarcinoma (HCC). Surprisingly, in silico analysis indicated that let-7 miRNA expression levels are not reduced in glioblastoma (GBM). Here we investigated the molecular basis of this differential expression. Using human GBM U87 and U251 cells, we first demonstrated that forced over-expression of MYC indeed could not down-regulate the expression of human MC-let-7a-1~let-7d microRNA cluster in GBM. Furthermore, analysis of MC-let-7a-1~let-7d promoter in GBM indicated that MYC failed to inhibit the promoter activity. Pearson's correlation and Linear Regression analysis using the expression data from GSE55092 (HCC) and GSE4290 (GBM) demonstrated a converse relationship of MC-let-7a-1~let-7d and MYC only in HCC but not in GBM. To understand the underlying mechanisms, we examined whether MYC could bind to the non-canonical E-box 3 located in the promoter of MC-let-7a-1~let-7d. Results from both chromatin immune-precipitation (ChIP) and super-shift assays clearly demonstrated the loss of MYC and E-box 3 binding in GBM, suggesting for the first time that a defective MYC and E-box3 binding in GBM is responsible for the differential MYC mediated transcriptional inhibition of MC-let-7a-1~let-7d and potentially other tumor suppressors. MYC and let-7 are key oncoprotein and tumor suppressor, respectively. Understanding the molecular mechanisms of their regulations will provide new insight and have important implications in the therapeutics of GBM as well as other cancers.